Modern large aircraft typically have a number of separate fuel tanks, the quantity of fuel in each tank being monitored and controlled in flight by a computerised fuel management system. Before an aircraft can be allowed to depart from an airport the pilot of the aircraft must be confident that the quantity of fuel on board the aircraft is sufficient to reach the intended destination. Ordinarily the information required concerning the quantity of fuel on board the aircraft to satisfy this requirement is provided by the fuel management system, based on fuel quantity readings from each of the individual fuel tanks. During flight the fuel quantity readings from each of the individual tanks are used, with other parameters, to calculate the gross weight centre of gravity of the aircraft at any given time and to perform automatic transfers of fuel between the individual fuel tanks to maintain the centre of gravity within desired limits. In accordance with known procedures, in the event of a failure within the fuel management system resulting in the quantity fuel within one of the individual fuel tanks becoming unknown, either whilst the aircraft is on the ground or during flight, the automatic control of a transfer of fuel between the individual fuel tanks by the fuel management system ceases since a total value for the amount of fuel on board the aircraft is no longer to the fuel management system. However, a dispatch of the aircraft or the continued flight of the aircraft is permitted provided that the aircraft crew perform manual fuel transfers based on manually performed calculations of the amount of fuel on board at a given time. This has the disadvantage of increasing the crew workload and, since the fuel calculations and transfers are subject to human error, decreasing the aircraft safety. It would therefore be advantageous to provide an alternative fuel management system and method of operation thereof that addresses these disadvantages.